Fig. 6.

Dispersion relation. The homogeneous state becomes unstable against periodic perturbations in a finite range of dimensionless wave numbers k (k = 2πλ₂/λ, where λ is the wavelength of the perturbation) for the following parameters: G₁/G₂ = –0.8 and D₂/D₁ = 100. The typical time of occurrence 1/w (w is the growth rate) is an ionic diffusive one. The instability appears at a finite wavelength and not at k = 0 as in other electrodynamic instabilities. This instability is analogous to the Turing instability.